Engine emissions control system

ABSTRACT

An engine emissions control system may include an electronic control module and a nitrogen oxide sensor in communication with the electronic control module. The nitrogen oxide sensor may be mounted on an exhaust system of an engine and may be configured to provide the electronic control module with feedback indicative of an actual level of nitrogen oxide in an exhaust stream flowing through the exhaust system. The engine emissions control system may also include an engine parameter adjustment assembly controlled by the electronic control module. The electronic control module may automatically actuate the engine parameter adjustment assembly to adjust an engine flow until the actual level of nitrogen oxide reaches a desired level of nitrogen oxide.

TECHNICAL FIELD

The present disclosure relates generally to internal combustion engine assemblies, and relates more particularly to a control system for regulating emissions produced by internal combustion engines.

BACKGROUND

Engines, including diesel engines, gasoline engines, gaseous fuel engines, and other engines known in the art, may generally be designed to combust processed fuels. There are, however, exceptions. For example, some gaseous fuel engines, like those used in wellhead applications, compressor stations, and generator set applications, may run on raw or unprocessed fuels. For example, a gaseous fuel engine that pumps gas from an underground source into a pipeline may be fueled by a quantity of that gas that is diverted from the pipeline into the fuel inlet of the engine. Since these fuels are raw or unprocessed, their qualities and compositions may vary widely depending on factors such as location and environment. As a consequence, gaseous fuel engines may typically be designed to run on a wide variety of gaseous fuels, so that a single engine may be used in a variety of conditions.

When a quantity of gaseous fuel is combusted in a combustion cylinder of a gaseous fuel engine, pollutants may be produced as byproducts of the combustion reaction. The pollutants may exit from the combustion cylinder as exhaust. Due to environmental concerns, governments have set restrictions on exhaust stream pollutants. One type of pollutant restricted by government regulations is nitrogen oxide (“NOx”). Controlling the amount of NOx produced by gaseous fuel engines may be particularly difficult because the quality and composition of the gaseous fuels may be inconsistent. Different gaseous fuels, or similar gaseous fuels with different concentrations of elements, may combust at different temperatures, and as a result, the amount of NOx produced by combusting a quantity of one fuel may be different than the amount produced by combusting the same quantity of another fuel. In order to ensure that these internal combustion engines meet government regulations, adjustments may have to be made to the engines on-site when the engines are used in new places, or when the quality or composition of the gaseous fuel at a site changes. These adjustments may be costly and time-consuming.

At least one system has been developed to control the amount of NOx in the exhaust stream of a gaseous fuel internal combustion engine. For example, U.S. Pat. No. 6,581,571 to Kubesh et al. (“Kubesh”) discloses a control system and method that uses a NOx sensor to provide a signal representing the amount of NOx in engine exhaust to an electronic engine control unit. Based on the signal, the electronic engine control unit controls set points, such as spark timing, air-fuel ratio, boost, intake temperature, or load. These set points may be varied to produce a change in the amount of NOx. However, NOx production may be dependent on a number of other parameters. Thus, the system and method in Kubesh may not be capable of adequately regulating NOx production by controlling those other parameters.

The system of the present disclosure is directed towards overcoming one or more of the constraints set forth above.

SUMMARY OF THE INVENTION

In one aspect, the presently disclosed embodiments may be directed to an engine emissions control system that may include an electronic control module and a nitrogen oxide sensor in communication with the electronic control module. The nitrogen oxide sensor may be mounted on an exhaust system of an engine, and may be configured to provide the electronic control module with feedback indicative of an actual level of nitrogen oxide in an exhaust stream flowing through the exhaust system. The engine emissions control system may also include an engine parameter adjustment assembly controlled by the electronic control module. The electronic control module may automatically actuate the engine parameter adjustment assembly to adjust an engine flow until the actual level of nitrogen oxide reaches a desired level of nitrogen oxide.

In another aspect, the presently disclosed embodiments may be directed to a method of controlling engine emissions. The method may include monitoring nitrogen oxide levels in an exhaust stream of an engine using a nitrogen oxide sensor. The method may also include transmitting a signal indicative of an actual nitrogen oxide level from the nitrogen oxide sensor to an electronic control module. The method may further include comparing the actual nitrogen oxide level to a desired nitrogen oxide level. The method may further include automatically adjusting an engine flow until the actual nitrogen oxide level reaches the desired nitrogen oxide level.

In another aspect, the presently disclosed embodiments may be directed to an engine assembly. The engine assembly may include an engine, and an engine emissions control system configured to automatically regulate the nitrogen oxide level in an exhaust stream of the engine. The control system may include an electronic control module, and a nitrogen oxide sensor in communication with the electronic control module. The nitrogen oxide sensor may be mounted on an exhaust system of an engine and may be configured to provide the electronic control module with feedback indicative of an actual level of nitrogen oxide in an exhaust stream flowing through the exhaust system. The control system may also include an engine parameter adjustment assembly controlled by the electronic control module, wherein the electronic control module may automatically actuate the engine parameter adjustment assembly to adjust an engine flow until the actual level of nitrogen oxide reaches a desired level of nitrogen oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an engine assembly according an exemplary embodiment of the present disclosure.

FIG. 2 is a schematic diagram of an engine assembly according to another exemplary embodiment of the present disclosure.

FIG. 3 is a schematic diagram of an engine assembly according to yet another exemplary embodiment of the present disclosure.

FIG. 4 is an enlarged view of a NOx sensor, according to an exemplary embodiment of the present disclosure.

FIG. 5 is an enlarged view of a NOx sensor, according to another exemplary embodiment of the present disclosure.

FIG. 6 is a flow diagram of a method of controlling engine emissions according to an exemplary embodiment of the present disclosure.

FIG. 7 is a flow diagram of a method of controlling engine emissions according to another exemplary embodiment of the present disclosure.

FIG. 8 is a flow diagram of a method of controlling engine emissions according to yet another exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

As shown in FIG. 1, engine assembly 10 may include an internal combustion engine 12, such as, for example, a diesel engine, a gasoline engine, or a gaseous fuel engine. Engine 12 may include an intake manifold 14 for receiving air, fuel, and/or exhaust flows, or any combination thereof. Engine 12 may also include one or more combustion cylinders (not shown) within which the air and fuel may be combusted, and an exhaust manifold 16 for allowing an exhaust stream to exit from the combustion cylinders and from engine 12.

In operation, engine performance may be dependent on one or more operational parameters. An example of one parameter is air-fuel ratio (“AFR”). AFR refers to the ratio of air to fuel present in the combustion cylinders of engine 12 during combustion. For performance reasons, engine 12 may operate at or near stoichiometric ratio. The stoichiometric ratio may refer to the point where just enough air is present during combustion to burn the available fuel. However, combustion temperatures at stoichiometric ratio may also be high, resulting in increased NOx production in the combustion cylinders. Increasing the AFR may help to decrease NOx production by reducing the combustion temperature in the combustion cylinders.

Engine assembly 10 may also include a turbocharger 18. Turbocharger 18 may include an exhaust-gas driven compressor 20 for compressing a quantity of air, fuel, exhaust, or any combination thereof, before it enters intake manifold 14. Compressing these gases may help boost engine performance. Compressor 20 may be coupled to a turbine 22 by a shaft 24. Turbine 22 may receive exhaust flow exiting from exhaust manifold 16, and turbine 22 may rotate as the exhaust flow passes through it. The rotation of turbine 22 may drive compressor 20, allowing it to compress air supplied by an air intake 64 through a flow conduit 66. Increasing the exhaust flow across turbine 22 may increase the power to compressor 20, while decreasing the exhaust flow across turbine 22 may have the opposite effect. Compressed gases may exit from compressor 20 through a flow conduit 26.

Engine assembly 10 may further include a fuel intake 28. Fuel intake 28 may include a fuel supply (not shown) and a fuel flow conduit 30 for directing the fuel from the fuel supply into engine 12. The fuel may include, for example, gasoline, diesel, natural gas, and/or any other suitable gaseous or liquid fuel. In this particular embodiment, fuel intake 28 may be positioned downstream from compressor 20. Since compressor 20 may generate pressure in flow conduit 26, fuel intake 28 may have to provide a high pressure fuel flow so that the fuel may be capable of overcoming the pressure in flow conduit 26 to enter intake manifold 14. Alternatively, fuel intake 28 and flow conduit 30 may be moved upstream from compressor 20 to a location at or near flow conduit 66. In that case, fuel intake 28 may only have to provide a low pressure fuel flow because it will not have to overcome the compressor pressure. It is also contemplated that high pressure fuel can be injected directly into the combustion cylinder as in a direct injected or prechambered engine.

An exhaust system 32 of engine assembly 10 may include a flow conduit 34, exhaust filtration devices (not shown), cooling devices (not shown), and/or a tailpipe assembly (not shown). Exhaust system 32 may receive exhaust flow from turbine 22 via flow conduit 34.

A wastegate 36 may be provided in engine assembly 10. Wastegate 36 may be fluidly coupled to flow conduits 38 and 40, and may include a wastegate valve (not shown). The wastegate valve may include a ball valve, a butterfly valve, a globe valve, and/or any other suitable valve device. Wastegate 36 may be adjusted toward an open position, increasing exhaust flow in flow conduits 38 and 40; a closed position, blocking exhaust flow from entering flow conduits 38 and 40; and positions between open and closed to restrict exhaust flow in flow conduits 38 and 40. It is also contemplated that wastegate 36 may be actuated into position by a mechanical actuator, electrical actuator, pneumatic actuator, or any other suitable actuator known in the art.

A NOx sensor 42 may be mounted on flow conduit 34, and may be configured to detect the level of NOx in the exhaust flow passing through flow conduit 34. At least a portion of NOx sensor 42 may extend through the wall of flow conduit 34 into the exhaust flow. In order to withstand the high temperatures in flow conduit 34, NOx sensor 42 may be constructed, for example, out of ceramic type metal oxides or any other suitable material. NOx sensor 42 may sample the exhaust for NOx, and convert that sensed value into a signal indicative of the NOx level therein.

Engine assembly 10 may also include an electronic control module (“ECM”) 44. ECM 44 may include an electronic system, such as, for example, an on-board computer having a processor for performing calculations, executing functions, and accessing information from a memory location. The memory location may include one or more databases used to store engine information, such as, for example, engine parameters and desired NOx levels. ECM 44 may be configured to communicate with wastegate 36, and one or more sensors, including NOx sensor 42, using communication links 46 and 48. Through communication link 46, ECM 44 may receive feedback from NOx sensor 42 in the form of signals indicative of the actual level of NOx in the exhaust. ECM 44 may compare the actual NOx level to the desired NOx level in order to determine if the actual NOx level is acceptable. ECM 44 may also communicate with temperature, pressure, fuel, and/or other sensors (not shown) known in the art that may be placed throughout engine assembly 10.

If ECM 44 determines that the actual NOx level is unacceptable, then ECM 44 may take corrective action by adjusting one or more engine parameters. If, for example, ECM 44 determines that the actual NOx level is excessive, it may adjust wastegate 36 toward a closed position. As a result, exhaust may be directed toward turbine 22 to speed up compressor 20, thus increasing air flow to intake manifold 14. Increasing air flow, while maintaining a relatively consistent fuel flow, may increase the AFR and bring down the combustion temperature in the combustion cylinders. NOx production decreases as the combustion temperature decreases, resulting in less NOx production.

If, however, ECM 44 determines that the NOx level is less than the desired level, then ECM 44 may adjust wastegate 36 toward an open position to direct exhaust flow away from turbine 22, causing turbine 22 to provide less power for running compressor 20. Accordingly, compressor 20 may supply less air to engine 12, resulting in a decrease in AFR. Combustion temperatures in the combustion cylinders may rise, but engine performance and efficiency may increase. Thus, NOx sensor 42, ECM 44, and wastegate 36 may help control emissions by balancing the competing considerations of engine performance and NOx production.

As shown in FIG. 2, engine assembly 10 may include an exhaust induction assembly 50. Exhaust induction assembly 50 may assist in directing treated or untreated exhaust to engine assembly 10. In one embodiment, exhaust induction assembly 50 may include a clean exhaust induction (“CEI”) assembly. However, it should be understood that any other suitable exhaust induction assembly, such as a dirty or untreated exhaust induction assembly, may also be used.

Exhaust induction assembly 50 may communicate with ECM 44 through a communication link 56. Exhaust induction assembly 50 may include an exhaust induction valve 51, such as, for example, a ball valve, a butterfly valve, a globe valve, and/or any other suitable valve device that is movable by an actuator (not shown). Exhaust induction assembly 50 may adjust an engine parameter, and in particular, the quantity of exhaust flow directed into engine 12. It is also contemplated that an exhaust treatment device (not shown) may be included in engine assembly 10 between turbine 22 and exhaust induction assembly 50. The exhaust treatment device may include, for example, a filter and/or a catalyst, for removing NOx, soot, particulate matter, and other pollutants from an exhaust stream.

When ECM 44 determines that the level of NOx in the exhaust flow in flow conduit 34 does not match the desired level, based at least in part on signals sent by NOx sensor 42, ECM 44 may adjust exhaust induction assembly 50 to achieve equality between the actual and desired values. For example, exhaust induction valve 51 may be adjusted toward an open position to increase the exhaust flow in flow conduits 52 and 54, thus directing exhaust into the upstream side of compressor 20. The exhaust may mix with air from air intake 64 and fuel from fuel intake 28, undergo compression in compressor 20, and pass through flow conduit 26 into intake manifold 14 and the combustion cylinders of engine 12. While the relative proportions of air and fuel in the combustion cylinders may be maintained, the added exhaust may act as an inert gaseous heat sink, lowering the combustion temperatures inside of the combustion cylinders by absorbing heat. Lowering the combustion temperatures may help to reduce NOx formation. It should be understood that exhaust induction valve 51 may be adjusted toward a closed position to reduce the amount of exhaust in the combustion cylinders, which may help engine performance while also increasing the combustion temperature in the combustion cylinders. However, ECM 44 and exhaust induction valve 51 may help to ensure that the actual NOx level will not exceed the desired level by adding exhaust to lower the combustion temperature when required.

Directing exhaust flow into intake manifold 14 using exhaust induction assembly 50 may increase the density of the gas mixture entering intake manifold 14. The density of this mixture may be referred to as the “charge density.” In general, a higher charge density may result in lower NOx production, while a lower charge density may have the opposite effect. However, excessive charge density may result in misfires, while insufficient charge density may cause engine knock. Thus, the quantity of the exhaust flow set by ECM 44 and exhaust induction assembly 50 may be selected so that the charge density may be low enough to avoid misfires, but high enough to prevent engine knock, while also keeping the actual NOx level in line with the desired level.

As shown in FIG. 3, emissions produced by engine assembly 10 may be provided with a control system including ECM 44, NOx sensor 42, and fuel intake 28. In this embodiment, fuel intake 28 may include a fuel metering valve 29 actuatable by an actuator to a closed position, an open position, and intermediate positions therebetween, for controlling the quantity of fuel supplied to engine 12. Fuel metering valve 29 may include a ball valve, a butterfly valve, a globe valve, and/or any other suitable valve device. The actuator may include a mechanical, electrical, and/or pneumatic actuator, or the like. If ECM 44 determines that the level of NOx in the exhaust is not equal to the desired level, based at least in part on the signals provided by NOx sensor 42, ECM 44 may, through a communication link 58, instruct fuel intake 28 to alter the quantity of fuel flow until the levels are equal or otherwise acceptable. For example, by adjusting fuel metering valve 29 toward a closed position, fuel flow to the combustion cylinders of engine 12 may decrease, thus increasing the AFR in the combustion cylinders. The increase in the AFR may correspond to a decrease in the combustion temperature in the combustion cylinders, and a decrease in NOx production as well. If, on the other hand, the actual NOx level is less than the desired level, ECM 44 may adjust fuel metering valve 29 toward an open position to increase the quantity of fuel flow, thus decreasing the AFR and boosting engine performance. However, the combustion temperature in the combustion cylinders may also increase, causing a rise in NOx production. ECM 44 may set fuel intake 28 at the point where the actual NOx level equals the desired level. Thus, ECM 44 may seek to strike a balance between engine performance and NOx reduction.

While the elements of the control systems shown in FIGS. 1-3 are described separately, it should be understood that each of the control systems may also be used in combination with one or more of the other control systems.

FIG. 4 shows an enlarged view of flow conduit 34 and NOx sensor 42. In this embodiment, NOx sensor 42 may continuously monitor exhaust flowing through flow conduit 34, and may continuously supply ECM 44 with NOx level readings. This embodiment may be used with in the embodiments of engine assembly 10 shown in FIGS. 1-3.

FIG. 5 shows another enlarged view of NOx sensor 42 and flow conduit 34. In this embodiment, a bypass line 60 having a bypass valve 62 may be fluidly coupled to flow conduit 34. When bypass valve 62 is opened, the exhaust from flow conduit may flow into bypass line 60. NOx sensor 42 may be mounted on bypass line 60, and at least a portion of NOx sensor 42 may be exposed to the exhaust flowing through bypass line 60 when bypass valve 62 is in an open position. Closing bypass valve 62 may prevent the exhaust from entering bypass line 60. Thus, this embodiment may provide for periodic monitoring of NOx levels in the exhaust stream with NOx sensor 42 being capable of monitoring the exhaust only when bypass valve 62 is open. ECM 44 may control bypass valve 62 using a communication link 68. It is contemplated that bypass valve 62 may include a ball valve, a butterfly valve, a globe valve, and/or any other suitable valve device, and a suitable actuator for moving bypass valve 62 into or out of closed position. This embodiment of NOx sensor 42 may be used in the embodiments of engine assembly 10 shown in FIGS. 1-3.

FIG. 6 shows an embodiment of a method for controlling engine assembly 10. The method may start (step 70) with determining the actual NOx level in the engine's exhaust (step 72). The actual level may be determined using, for example, NOx sensor 42, to take continuous or periodic readings of the exhaust, and then transmitting a signal indicative of the NOx level to ECM 44. ECM 44 may compare the actual NOx level to the desired level (step 74), and may adjust an engine parameter, in this case the AFR until the actual NOx level equals the desired level (step 76). ECM 44 may lower the actual NOx level by increasing the AFR by moving wastegate 36 toward a closed position so that a greater quantity of exhaust flow may be directed into turbine 22, causing compressor 20 to speed up and provide more air to intake manifold 14. As the AFR increases, the combustion temperature in the combustion cylinders of engine 12 may decrease, resulting in a decrease in NOx production. ECM 44 may move wastegate 36 toward an open position to divert exhaust flow away from turbine 22, causing compressor 20 to slow down and provide less air to intake manifold 14. Doing so may bring gains in efficiency and performance, but may also increase combustion temperature and NOx production. Once the desired level is achieved, the process may end (step 78). It is contemplated that this methodology may be used at least with engine assembly 10 from FIG. 1.

FIG. 7 shows another embodiment of a method for controlling engine assembly 10. The method may start (step 70) with determining the actual NOx level in the engine's exhaust (step 72). The actual level may be determined using, for example, NOx sensor 42, to take continuous or periodic readings of the exhaust, and then transmitting a signal indicative of the NOx level to ECM 44. ECM 44 may compare the actual NOx level to the desired level (step 74), and may adjust an engine parameter, in this case the exhaust flow, until the actual NOx level equals the desired level (step 80). ECM 44 may lower the actual NOx level by increasing the exhaust flow by adjusting exhaust induction valve 51 toward an open position, where a greater quantity of the exhaust flow may be directed into intake manifold 14. The exhaust flow may act as an inert, absorbing and carrying away heat from the combustion cylinders, resulting in decreased combustion temperatures and reduced NOx production. ECM 44 may adjust exhaust induction valve 51 toward a closed position, where the exhaust flow may be directed toward exhaust system 32 and out of engine assembly 10. This may help boost engine performance, while also increasing combustion temperature and NOx production. Once the desired level is achieved, the process may end (step 78). It is contemplated that this methodology may be used at least with engine assembly 10 from FIG. 2.

FIG. 8 shows another embodiment of a method for controlling engine assembly 10. The method may start (step 70) with determining the actual NOx level in the engine's exhaust (step 72). The actual level may be determined using, for example, NOx sensor 42, to take continuous or periodic readings of the exhaust, and then transmitting a signal indicative of the NOx level to ECM 44. ECM 44 may compare the actual NOx level to the desired level (step 74), and may adjust an engine parameter, in this case the fuel flow, until the actual NOx level equals the desired level (step 82). ECM 44 may lower the actual NOx level by adjusting fuel metering valve 29 toward a closed position to decrease the fuel flow to intake manifold 14. This may increase the AFR, and with less fuel for combustion, the combustion temperature of the combustion cylinders may also be reduced, resulting in decreased NOx production. ECM 44 may adjust fuel metering valve 29 toward an open position to increase the fuel flow to intake manifold 14. This may decrease the AFR and provide more fuel for combustion, resulting in increased combustion temperatures and increased NOx production. Once the desired level is achieved, the process may end (step 78). It is contemplated that this methodology may be used at least with engine assembly 10 of FIG. 3.

INDUSTRIAL APPLICABILITY

The disclosed engine assembly control system and method may have applicability in internal combustion engines. The system and method may have particular applicability with regard to controlling the NOx emissions produced by internal combustion engines.

Providing an internal combustion engine with the ability to regulate NOx production in a gaseous fuel internal combustion engine may be important for achieving government standards limiting NOx levels in engine emissions. In particular, the ability to adjust engine parameters (e.g. air flow, AFR, exhaust flow, charge density, and/or fuel flow) may allow engine assembly 10 to achieve those standards regardless of changes in fuel supply or the environment in which engine assembly 10 may be used. Thus, engine assembly 10 may be more robust and more capable of performing under a wide range of conditions.

Since engine assembly 10 may adjust engine parameters automatically, manual adjustment of engine assembly components may not be required, thus saving both time and money. Furthermore, by eliminating the need for manual adjustment, the need to tamper with engine assembly 10 may be eliminated. As tampering may be detrimental to the life and performance of engine assembly 10, eliminating it may be beneficial.

Furthermore, NOx sensors may be subjected to harsh conditions due to their placement in or near high temperature exhaust streams. By mounting a NOx sensor 42 on a bypass line 60, wear and tear on NOx sensor 42 may be reduced because its exposure to the exhaust stream may be periodic rather than continuous. Reducing wear on NOx sensor 42 may extend its useful life, and may improve its accuracy.

It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system and method without departing from the scope of the disclosure. Additionally, other embodiments of the disclosed system and method will be apparent to those skilled in the art from consideration of the specification. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure. 

1. An engine emissions control system, comprising: an electronic control module; a nitrogen oxide sensor in communication with the electronic control module, wherein the nitrogen oxide sensor is mounted on an exhaust system of an engine, and is configured to provide the electronic control module with feedback indicative of an actual level of nitrogen oxide in an exhaust stream flowing through the exhaust system; and an engine parameter adjustment assembly controlled by the electronic control module, wherein the electronic control module automatically actuates the engine parameter adjustment assembly to adjust an engine flow until the actual level of nitrogen oxide reaches a desired level of nitrogen oxide.
 2. The control system of claim 1, wherein the engine parameter adjustment assembly includes a wastegate valve, and the engine flow is an intake air flow.
 3. The control system of claim 1, wherein the engine parameter adjustment assembly includes an exhaust induction valve, and the engine flow is an exhaust flow.
 4. The control system of claim 1, wherein the engine parameter adjustment assembly includes a fuel metering valve, and the engine flow is a fuel flow.
 5. The control system of claim 1, wherein the engine is a gaseous fuel internal combustion engine.
 6. The control system of claim 1, wherein the nitrogen oxide sensor is continuously exposed to the exhaust stream.
 7. The control system of claim 1, wherein the nitrogen oxide sensor is periodically exposed to the exhaust stream.
 8. The control system of claim 7, wherein the nitrogen oxide sensor is mounted on a bypass line, and the nitrogen oxide sensor is exposed to the exhaust stream by moving a bypass valve of the bypass line to an open position.
 9. A method of controlling engine emissions, comprising: monitoring nitrogen oxide levels in an exhaust stream of an engine using a nitrogen oxide sensor; transmitting a signal indicative of an actual nitrogen oxide level from the nitrogen oxide sensor to an electronic control module; comparing the actual nitrogen oxide level to a desired nitrogen oxide level; and automatically adjusting an engine flow until the actual nitrogen oxide level reaches the desired nitrogen oxide level.
 10. The method of claim 9, wherein automatically adjusting the engine flow includes operating a wastegate valve to adjust intake air flow into the engine.
 11. The method of claim 9, wherein automatically adjusting the engine flow includes operating an exhaust induction valve to adjust exhaust flow into the engine.
 12. The method of claim 9, wherein automatically adjusting the engine flow includes operating a fuel metering valve to adjust fuel flow into the engine.
 13. An engine assembly, comprising: an engine; and an engine emissions control system configured to automatically regulate the nitrogen oxide level in an exhaust stream of the engine, wherein the control system includes: an electronic control module; a nitrogen oxide sensor in communication with the electronic control module, wherein the nitrogen oxide sensor is mounted on an exhaust system of an engine, and is configured to provide the electronic control module with feedback indicative of an actual level of nitrogen oxide in an exhaust stream flowing through the exhaust system; and an engine parameter adjustment assembly controlled by the electronic control module, wherein the electronic control module automatically actuates the engine parameter adjustment assembly to adjust an engine flow until the actual level of nitrogen oxide reaches a desired level of nitrogen oxide.
 14. The engine assembly of claim 13, wherein the engine parameter adjustment assembly includes a wastegate valve, and the engine flow is an intake air flow.
 15. The engine assembly of claim 13, wherein the engine parameter adjustment assembly includes an exhaust induction valve, and the engine flow is an exhaust flow.
 16. The engine assembly of claim 13, wherein the engine parameter adjustment assembly includes a fuel metering valve, and the engine flow is a fuel flow.
 17. The engine assembly of claim 13, wherein the engine is a gaseous fuel internal combustion engine.
 18. The engine assembly of claim 13, where the nitrogen oxide sensor is continuously exposed to the exhaust stream.
 19. The engine assembly of claim 13, wherein the nitrogen oxide sensor is periodically exposed to the exhaust stream.
 20. The engine assembly of claim 19, wherein the nitrogen oxide sensor is mounted on a bypass line, and the nitrogen oxide sensor is exposed to the exhaust stream by moving a bypass valve of the bypass line to an open position. 